1. Field of the Invention
The present invention relates to a system and method for installing a production casing along an inverted underground arcuate path beneath and spanning an obstacle such as a river, and in particular to such as system and method for spanning extremely wide obstacles.
2. Description of the Prior and Contemporaneous Art
Techniques have recently been developed for installing relatively large diameter production casings beneath rivers and other obstacles without dredging the riverbed or otherwise affecting the obstacle itself. Instead, a pilot hole is first drilled along an inverted underground arcuate path from a position at or near ground level on one side of the obstacle to a position at or near ground level on the other side. After drilling the pilot hole, the pilot drill string remains in the hole. A reamer is then attached to one end of the drill string and is drawn or forced through the pilot hole to ream the pilot hole to a preselected larger diameter. The production casing or other large diameter casing is advanced into the reamed pilot hole in following relationship to the reaming apparatus. As a result, when the pilot hole has been reamed from one end to the other, the larger casing occupies the reamed hole.
The above techniques for placing production casings beneath obstacles have run into difficulties when relatively wide obstacles, such a major rivers, are to be traversed. The path of the production casing is generally horizontal, and the weight of the casing, and therefore the friction which must be overcome when it is moved, increases proportionate to the width of the obstacle. The casing can be sealed to make it buoyant in an attempt to counterbalance the weight of the casing, but it is extremely difficult to exactly balance the weight when long production casings are being installed. As a result, friction forces on the casing increase, and when a wide obstacle is to be traversed, the casing will eventually become frozen or substantially impeded by the friction between the casing and the reamed pilot hole and it will not completely span the obstacle.